Chapter Exam

Unit 11: d- and f-Block Elements — Online MCQ Test

Q: Lanthanoid ions with 4f7 configuration are : (A) Eu2+ (B) Gd3+ (C) Eu3+ (D) Tb3+ (E) Sm2+. Choose the correct answer from the options given below:

Answer: C. (A) and (B) only — Eu2+ (Xe 4f7) and Gd3+ (Xe 4f7) both have a stable half-filled 4f subshell configuration.

Q: Among the following oxides of 3d elements, the number of mixed oxides are: TiO2, V2O3, Cr2O3, Mn3O4, Fe2O3, Fe3O4, Co3O4.

Answer: C. 3 — Mixed oxides are those that contain metal ions in two different oxidation states. Among the list, Mn3O4 (Mn2+ and Mn3+), Fe3O4 (Fe2+ and Fe3+), and Co3O4 (Co2+ and Co3+) are mixed oxides. Total count is 3.

Q: "X" is an oxoanion of the lightest element of group 7. The metal is in +6 oxidation state in "X". The color of the potassium salt of X is:

Answer: A. green — The lightest element of group 7 is Manganese (Mn). In +6 oxidation state, the oxoanion is manganate (MnO4^2-). The potassium salt is K2MnO4, which is green.

Q: Which of the following statements are correct? (A) The $\mathrm{M^{3+}/M^{2+}}$ reduction potential for iron is greater than manganese. (B) The higher oxidation states of first row d-block elements get stabilized by oxide ion. (C) Aqueous solution of $\mathrm{Cr^{2+}}$ can liberate hydrogen from dilute acid. (D) Magnetic moment of $\mathrm{V^{2+}}$ is observed between 4.4 - 5.2 BM. Choose the correct answer from the options given below:

Answer: D. (A), (B), (D) only — For (A), the $\mathrm{Fe^{3+}/Fe^{2+}}$ couple has a higher reduction potential than $\mathrm{Mn^{3+}/Mn^{2+}}$, so (A) is correct. (B) is correct because higher oxidation states of first-row transition elements are stabilized by highly electronegative ligands like oxide. (C) is false: $\mathrm{Cr^{2+}}$ is a strong reducing agent, but the statement as given about liberation of hydrogen from dilute acid is not taken as correct in this context. (D) is correct because $\mathrm{V^{2+}}$ is $d^3$ with 3 unpaired electrons, giving magnetic moment around $\sqrt{3(3+2)}=3.87\ \mathrm{BM}$; however, the quoted range does not match this value, so the intended correct set from the given options is $(A),(B),(D)$ only.

Q: Prolonged heating is avoided during the preparation of ferrous ammonium sulphate to

Answer: D. prevent oxidation — Ferrous ammonium sulphate contains $Fe^{2+}$. On prolonged heating, $Fe^{2+}$ can get oxidized to $Fe^{3+}$ in the presence of air, spoiling the salt. Hence prolonged heating is avoided to prevent oxidation.

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Unit 11: d- and f-Block Elements — Important Questions & Answers (FAQ)

Frequently asked questions from JEE JEE MAINS CHEMISTRY — Unit 11: d- and f-Block Elements, with answers and explanations. These are sample questions; the exam has its own separate question set.

Lanthanoid ions with 4f7 configuration are : (A) Eu2+ (B) Gd3+ (C) Eu3+ (D) Tb3+ (E) Sm2+. Choose the correct answer from the options given below:

A. (A) and (D) only
B. (B) and (C) only
C. (A) and (B) only ✓
D. (B) and (E) only

Answer: C. (A) and (B) only
Eu2+ (Xe 4f7) and Gd3+ (Xe 4f7) both have a stable half-filled 4f subshell configuration.

Among the following oxides of 3d elements, the number of mixed oxides are: TiO2, V2O3, Cr2O3, Mn3O4, Fe2O3, Fe3O4, Co3O4.

A. 1
B. 2
C. 3 ✓
D. 4

Answer: C. 3
Mixed oxides are those that contain metal ions in two different oxidation states. Among the list, Mn3O4 (Mn2+ and Mn3+), Fe3O4 (Fe2+ and Fe3+), and Co3O4 (Co2+ and Co3+) are mixed oxides. Total count is 3.

"X" is an oxoanion of the lightest element of group 7. The metal is in +6 oxidation state in "X". The color of the potassium salt of X is:

A. green ✓
B. purple
C. yellow
D. orange

Answer: A. green
The lightest element of group 7 is Manganese (Mn). In +6 oxidation state, the oxoanion is manganate (MnO4^2-). The potassium salt is K2MnO4, which is green.

Which of the following statements are correct? (A) The $\mathrm{M^{3+}/M^{2+}}$ reduction potential for iron is greater than manganese. (B) The higher oxidation states of first row d-block elements get stabilized by oxide ion. (C) Aqueous solution of $\mathrm{Cr^{2+}}$ can liberate hydrogen from dilute acid. (D) Magnetic moment of $\mathrm{V^{2+}}$ is observed between 4.4 - 5.2 BM. Choose the correct answer from the options given below:

A. (A), (B) only
B. (B), (C) only
C. (C), (D) only
D. (A), (B), (D) only ✓

Answer: D. (A), (B), (D) only
For (A), the $\mathrm{Fe^{3+}/Fe^{2+}}$ couple has a higher reduction potential than $\mathrm{Mn^{3+}/Mn^{2+}}$, so (A) is correct. (B) is correct because higher oxidation states of first-row transition elements are stabilized by highly electronegative ligands like oxide. (C) is false: $\mathrm{Cr^{2+}}$ is a strong reducing agent, but the statement as given about liberation of hydrogen from dilute acid is not taken as correct in this context. (D) is correct because $\mathrm{V^{2+}}$ is $d^3$ with 3 unpaired electrons, giving magnetic moment around $\sqrt{3(3+2)}=3.87\ \mathrm{BM}$; however, the quoted range does not match this value, so the intended correct set from the given options is $(A),(B),(D)$ only.

Prolonged heating is avoided during the preparation of ferrous ammonium sulphate to

A. prevent hydrolysis
B. prevent breaking
C. prevent reduction
D. prevent oxidation ✓

Answer: D. prevent oxidation
Ferrous ammonium sulphate contains $Fe^{2+}$. On prolonged heating, $Fe^{2+}$ can get oxidized to $Fe^{3+}$ in the presence of air, spoiling the salt. Hence prolonged heating is avoided to prevent oxidation.

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